COMMENT:
Alex's parents were in London the two days before the second bombing and there was no security to speak of. The day before the bombing on the tube, security was massively beefed up, with hundreds of police and bomb-sniffing dogs. This confirms that they had some kind of warning and increased security ahead of the second bombing attempt.

SCOTLAND Yard knew the Tube would be bombed yesterday after being tipped off there would be an attack this week, it emerged last night.

Mr Clarke gave the confidential briefing immediately after Tony Blair had chaired a full cabinet meeting in Downing Street.

A senior No10 source said: "Charles Clarke made it very clear there would be further attacks and that further incidents were a strong likelihood."

After officers missed nabbing the Farringdon suspect, warning memos are believed to have been sent to transport workers to be on the lookout for a tall, Middle-Eastern man.

Signs of the heightened security on the London Underground network were clear yesterday morning before the bombers struck.

There was a heavy, visible armed police presence in and around stations.

At Westminster station tourists were asked to take off backpacks and line them up against walls.

And in anti-suicide bomber procedures similar to those used in Iraq, sniffer dogs were brought in to smell the bags for possible explosives.

One eyewitness at the station said: "I have never seen anything like that in London before, even after the July 7 bombings.

"There were at least eight officers, including several with machine guns, just at one underground station."

At Westminster and other Government buildings the terror alert was on "amber", meaning a "substantial threat to UK interests".

There is only one higher state of alert, red, which means a major target such as Parliament or the transport system is "believed to be the target of an imminent terrorist attack".

In the cabinet briefing, the Home Secretary hinted at fears there could be copycat attacks in the wake of the July 7 atrocities.

But a senior Home Office source last night insisted yesterday's attacks were linked to al-Qaeda. The source said: "There's no doubt it was the same inspiration as on July 7.

"What we don't understand at this stage is why there was such a difference in effectiveness.

"It raises the possibility that this was a related organisation rather than the same one that carried out the earlier attacks."

Police are working on the possibility that a semi-formed terror cell unconnected with the Leeds-based suicide fanatics may have been behind yesterday's attempted atrocities.

They think the terrorists may have not yet been fully trained but were sent into action anyway.

Meanwhile, a former British intelligence officer who cannot be named said: "This attack is a major breakthrough. Police and security services now probably have four bombing devices which, although crude, will be a goldmine of evidence.

"They will almost certainly tell us a lot about the background of the bomb-maker, where that person learned his craft and who taught them.

"If this was a terrorist attack by twisted fanatics, someone made a very big mistake.

"And in the wake of that mistake there may a lot of very important evidence and some very worried international terrorists.